Thermoplastic elastomer compositions

Abstract

The invention relates to polymer compositions useful as thermoplastic elastomers for extrusion, calendering, blow molding, thermoforming, and foam processing, and to articles made therefrom. Such improved melt strength thermoplastic elastomers include a blend of propylenic resin (A) and ethylenic elastomer (B), wherein the (A) resin is partially branched and/or the (B) elastomer is partially crosslinked by the addition of multifunctional acrylic monomer (C) containing at least three acrylate groups.

What is claimed is:  
     
       1. A thermoplastic elastomer composition comprising a modified blend of a propylenic resin, an ethylenic elastomer, and a multifunctional acrylic monomer that does not contain a methacrylate group comprising at least three acrylate groups, or a reaction product thereof, with the ethylenic elastomer being present in an amount by weight that is greater than that of the propylenic resin and wherein (a) the propylenic resin is at least partially branched, (b) the ethylenic elastomer is at least partially crosslinked to a gel content of at least about 25%, or (a) and (b), the modified blend having: 
       a ratio of the melt strength of the modified blend to the melt strength of an unmodified blend of a propylenic resin that is not branched and an ethylenic elastomer that is not crosslinked of about 1.5 to 15 measured at a temperature of at least about 180° C.;  
       a melt flow rate of less than about 1 dg/min measured at 230° C. under a 2.16 kg load;  
       a melt flow rate of less than about 5 dg/min measured at 230° C. under a 10 kg load; and  
       a hardness of less than about 95 Shore A or less than about 45 Shore D.  
     
     
       2. The composition of  claim 1 , wherein the ratio of the melt strength of the modified blend to the melt strength of the blend before modification is about 1.6 to 12 measured at a temperature of at least about 180° C. 
     
     
       3. The composition of  claim 1 , wherein the reaction of the propylenic resin, the ethylenic elastomer, and the multifunctional acrylic monomer is initiated by heat activation at a temperature of about 200° C. to 250° C. 
     
     
       4. The composition of  claim 1 , wherein the reaction of the propylenic resin, the ethylenic elastomer, and the multifunctional acrylic monomer is initiated by a free radical initiator present in an amount less than about 0.3 pph. 
     
     
       5. The composition of  claim 4 , wherein the free radical initiator has a decomposition half-life of greater than about one hour at 120° C. 
     
     
       6. The composition of  claim 1 , wherein the modified blend comprises about 5 weight percent to up to less than 50 weight percent propylenic resin and greater than 50 weight percent to about 95 weight percent of the ethylenic elastomer. 
     
     
       7. The composition of  claim 1 , wherein the modified blend comprises about 15 weight percent to 48 weight percent propylenic resin and about 52 weight percent to 85 weight percent of the ethylenic monomer. 
     
     
       8. The composition of  claim 1 , wherein the propylenic resin comprises at least about 60 mole percent propylene monomer and the ethylenic elastomer comprises at least 60 mole percent ethylene monomer. 
     
     
       9. The composition of  claim 1 , wherein the ethylenic elastomer has a Mooney viscosity of at least about 15, a weight average molecular weight of greater than about 80,000, and a polydispersity of greater than about 1.5. 
     
     
       10. The composition of  claim 1 , wherein the ethylenic elastomer has a density of less than 0.94 g/cm 3 . 
     
     
       11. The composition of  claim 1 , wherein the multifunctional acrylic monomer is present in an amount of about 0.1 pph to 5 pph of the polymers and has no more than seven acrylate groups. 
     
     
       12. The composition of  claim 4 , wherein the multifunctional acrylic monomer comprises trimethylolpropane triacrylate (TMPTA), ethoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, pentaerythritol triacrylate, bistrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, ethoxylated pentaerythritol tetraacrylate, ethoxylated pentaerythritol triacrylate, or combinations thereof. 
     
     
       13. The composition of  claim 1 , wherein the propylenic resin comprises a homopolymer of propylene or a copolymer of propylene and at least one monomer comprising C 2  to C 20  alpha-olefins, unsaturated organic acids, vinyl esters, aromatic vinyl compounds, vinylsilanes and unconjugated aliphatic and monocyclic diolefins, alicyclic diolefins which have an endocyclic bridge, conjugated aliphatic diolefins, and combinations thereof; and 
       wherein the ethylenic elastomer comprises a copolymer of ethylene and at least one monomer comprising C 3  to C 20  alpha-olefins, unsaturated organic acids, vinyl esters, aromatic vinyl compounds, vinylsilanes and unconjugated aliphatic and monocyclic diolefins, alicyclic diolefins which have an endocyclic bridge and conjugated aliphatic diolefins or terpolymers of at least 60 mole percent of ethylene, a C 3  to C 20  alpha-olefin, a nonconjugated diene monomer, or combinations thereof.  
     
     
       14. The composition of  claim 1 , further comprising one or more thermal stabilizers, ultraviolet stabilizers, flame retardants, mineral fillers, extender or process oils, conductive fillers, nucleating agents, plasticizers, impact modifiers, colorants, mold release agents, lubricants, antistatic agents, and pigments. 
     
     
       15. The composition of  claim 1  prepared by the process of melt blending the propylenic resin, the ethylenic elastomer, and the multifunctional acrylic monomer while initiating the reaction of each with at least one of heat activation or a free radical initiator. 
     
     
       16. An article comprising the composition of  claim 1 , which is formed by extrusion, thermoforming, blow molding, foam processing, or calendering. 
     
     
       17. The article of  claim 16  in the form of an automobile component. 
     
     
       18. The composition of  claim 1 , wherein the composition comprises about 25 to 45 weight percent propylenic resin, about 58 to 78 weight percent total ethylenic elastomer, a peroxide, a triacrylate, and a paraffinic oil. 
     
     
       19. A method for preparing the thermoplastic elastomer composition of  claim 1  comprising: 
       combining a propylenic resin that is at least partially branched, an ethylenic elastomer that is at least partially crosslinked, and a multifunctional acrylic monomer in the presence of an optional free radical initiator, to form a polymer mixture;  
       melt blending the polymer mixture at a temperature above the melt point of the propylenic resin and below about 180° C. for about 5 to 20 seconds; and  
       mixing the polymer mixture at a temperature of about 160° C. to 250° C. for at least about 10 to 100 seconds to provide a modified polymer blend as the thermoplastic elastomer composition.  
     
     
       20. The thermoplastic elastomer composition of  claim 1  further comprising a styrenic elastomer. 
     
     
       21. The composition of  claim 4 , wherein the free radical initiator is present in an amount of about 0.015 pph or less.